<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>第17题</title>
    <script>
        // 用户输入年份
        var n = parseInt(prompt("请输入一个年份","1999"));
        // 判断闰年条件
       if (n % 400 === 0 || n % 100 !== 0 && n % 4 === 0) {
           alert(n + "年是闰年");
       } else {
           alert(n + "年不是闰年");
       }
    </script>
</head>
<body>
    
</body>
</html>